1. Field of the Invention
The invention relates to gas-fired furnaces and more particularly to heat exchanger and plate assemblies for use in a gas-fired furnace.
2. Description of the Prior Art
Heat exchanger units for use in gas-fired furnaces generally include an opening in a lower pouch section for insertion of a gas burner, and an exit opening for flue gases in an upper section. A pouch plate and partition plate are generally secured over the pouch area and upper section respectively of each heat exchanger unit, after which the plates are secured in a leak proof joint to the sides of the furnace to isolate air heated by the heat exchangers in the rear of the furnace from furnace controls in the front.
It has been customary to weld the pouch plate and partition plate to the heat exchanger units. However, the welding operation is costly. Furthermore, the resulting structure lacks structural integrity because of stresses which are introduced during the welding process and which are aggravated by expansion and contraction of the metal of the heat exchanger unit during on and off cycles of the furnace. Another disadvantage of welding is the presence of noxious fumes which are produced during the welding process, and which result not only in a loss of comfort and healthful air in the vicinity of activity within a manufacturing facility, but result in an increased level of pollution of outside air into which the fumes must ultimately be expelled.
It has been proposed to avoid the need for welding by providing mounting flanges on the heat exchangers at the openings therein, and also on the pouch and partition plates, and then securing these flanges together with fastening means such as screws. However, this is a time consuming assembly technique which often results in distortion of the assembled parts. Also, the parts tend to work loose when subjected to expansion and contraction during on and off cycles of the furnace. Another technique, disclosed in U.S. Pat. Nos. 3,908,629 and 3,940,837 of The Singer Company, avoids welding by providing mounting flanges on the heat exchanger at the openings and folding such flanges back onto the plate members while entrapping sheet insulating material to complete the attachment and seal. However, such technique does not permit the application to heat exchangers of a brittle coating such as porcelain enamel, often times desirable for the purpose of enhancing corrosion resistant properties of heat exchangers and improving their heat transfer characteristics.
It is an object of this invention to provide an improved no-weld construction having high structural integrity for a heat exchanger unit and plate assembly.
It is another object of the invention to provide an improved no-weld construction for a heat exchanger unit and plate assembly wherein it is required that the heat exchanger unit shall include a brittle corrosion resistant and heat transfer coating.
It is still another object of the invention to provide an improved no-weld method of joining a heat exchanger unit to a plate at each of one or more pairs of aligned apertures in the unit and plate by expanding a flange on the plate within the aperture in the heat exchanger unit.
Other objects and advantages of the invention will become apparent hereinafter.